The present invention relates to a magnetic recording medium. More particularly, it relates to a magnetic recording medium, particularly of the type that the magnetic layer is kept in contact with the back coat layer, except recording and reproducing, such as a magnetic recording tape having a magnetic layer comprising a magnetic metal.
As magnetic recording media, there are known those having a magnetic layer comprising a magnetic metal oxide and those having a magnetic layer comprising a magnetic metal. In comparison with the former using a magnetic metal oxide, the latter using a magnetic metal is apt to be corroded. As the result of such corrosion, the saturation magnetization is decreased, the coefficient of friction is increased and the running stability is lowered. In case of those of vaporization type (i.e. those having a magnetic layer formed by vaporization of a magnetic metal), spotted rust is produced, and in case of those of an application type (i.e. those having a magnetic layer formed by application of a magnetic coating composition), the noise level is unfavorably increased. In addition, the running stability of those using a magnetic metal powder is greatly influenced by the lubricity at the surface of the magnetic layer.
In order to overcome the above problems as seen in a magnetic recording medium which comprises a support, a magnetic layer comprising a magnetic metal provided on one surface (i.e. the major surface) of the support and a back coat layer provided on the other surface (i.e. the back surface) of the support, it was proposed to incorporate a nitrogen-containing heterocyclic compound (e.g. benzotriazole, tolyltriazole) or a vaporizable aliphatic amine (e.g. diisopropylamine, octadecylamine, triethanolamine) into the back coat layer so as to improve the resistance of the magnetic layer to corrosion and enhance the running stability of the magnetic recording medium (cf. Japanese Patent Publication (unexamined) No. 122,621/83).
Incorporation of a nitrogen-containing heterocyclic compound into the back coat layer produces a considerable effect in improvement of the resistance of the magnetic layer to corrosion but shows no significant effect in enhancement of the running stability. Incorporation of an aliphatic amine produces a great effect in enhancement of the running stability but does not show any sufficient effect in improvement of the corrosion resistance. Incorporation of a nitrogen-containing heterocyclic compound and an aliphatic amine into the back coat layer was tried, but the produced effect for improvement of the corrosion resistance and enhancement of the running stability was poorer than that by their sole use.